Could Enlarged Sagittal Cervical Canal Diameter in Conventional Plain Lateral Radiographs Indicate the Presence of Syringomyelia? A Propensity Score Matched Study.

Abstract

Retrospective study. To investigate the correlation between sagittal cervical canal diameter on lateral whole spine radiographs and the incidence of syringomyelia in scoliosis patients. Neurosurgical evaluation and management are imperative in scoliosis patients with syringomyelia, as there is an increased risk of neurological deterioration during deformity correction surgery. Nevertheless, routine MRI screening is not indicated in scoliosis patients with a typical curve and normal neurology. Twenty-nine scoliosis patients with syringomyelia were grouped in Gp1, and 1029 adolescent idiopathic scoliosis (AIS) patients were grouped in Gp2. Propensity score matching (PSM) with one-to-one nearest neighbour matching (match tolerance 0.05) was performed. Twenty-eight pairs of patients were matched. Sagittal cervical canal diameter and the ratio between cervical canal/vertebral body were measured. Receiver-operating-characteristics (ROC) curves for both parameters were drawn to predict the incidence of syringomyelia. Sagittal canal diameter of C5 to C7 in Gp1 was significantly increased compared with Gp2 (C5: 17.78±3.61 vs. 16.32±1.18; P =0.047), (C6: 18.67±3.30 vs. 16.68±1.25; P =0.004), (C7: 18.99±3.24 vs. 17.06±1.17; P =0.004). The ratio between canal diameter/vertebral body in Gp1 was significantly increased compared with Gp2. (C5: 1.42±0.38 vs. 1.23±0.15; P =0.015), (C6: 1.47±0.35 vs. 1.22±0.14; P =0.001), (C7: 1.46±0.29 vs. 1.20±0.13; P <0.001). ROC analysis of C7 canal diameter showed acceptable discrimination of AUC 0.663 in predicting syringomyelia ( P =0.036). The cutoff value of 17.65 mm had a sensitivity of 60.7% and a specificity of 71.4%. C7 canal ratio showed excellent discrimination of AUC 0.794 in predicting syringomyelia ( P <0.001). The cutoff value of 1.22 had a sensitivity of 78.6% and a specificity of 71.4%. Sagittal cervical canal diameter measured in radiograph can be utilized as an effective screening tool in the diagnostic evaluation of syringomyelia. We propose C7 canal diameter of 17.65 mm or C7 ratio of 1.22 as an indication for MRI scan to rule out syringomyelia in scoliosis patients.